The SCID-hu mouse is a heterochimera, constructed by transplantation of human fetal lymphoid tissue into the congenitally immunodeficient C.Bl7 scid/scid (SCID) mouse. Previous studies have established and standardized infection of SCID-hu mice by HIV. Furthermore, antiviral compounds such as AZT have been shown to inhibit HIV in vivo in SCID-hu mice. In this proposal the investigators wish to determine if the passive administration of well-characterized antibodies or cytotoxic T lymphocytes that recognize defined HIV epitopes can prevent HIV infection or inhibit its replication in SCID-hu mice. If these studies are successful, this model may constitute a unique and valuable system to test the ability of antibodies or T cells to inhibit HIV in vivo. As such, it may guide the selection of T and B cell epitopes to be included in future vaccine formulations against HIV. This system may also be useful for the development of methods to stimulate selectively protective primary and secondary human immune responses to HIV and other antigens in SCID-hu mice.